Declaring/Defining ap_[u] Variables - 2021.2 English

Vitis High-Level Synthesis User Guide (UG1399)

Document ID
UG1399
ft:locale
English (United States)
Release Date
2021-12-15
Version
2021.2 English

There are separate signed and unsigned classes:

  • ap_int<int_W> (signed)
  • ap_uint<int_W> (unsigned)

The template parameter int_W specifies the total width of the variable being declared.

User-defined types may be created with the C/C++ typedef statement as shown in the following examples:

include "ap_int.h"// use ap_[u]fixed<> types

typedef ap_uint<128> uint128_t; // 128-bit user defined type
ap_int<96> my_wide_var; // a global variable declaration

The default maximum width allowed is 1024 bits. This default may be overridden by defining the macro AP_INT_MAX_W with a positive integer value less than or equal to 4096 before inclusion of the ap_int.h header file.

CAUTION:
Setting the value of AP_INT_MAX_W too High can cause slow software compile and runtimes.

Following is an example of overriding AP_INT_MAX_W:

#define AP_INT_MAX_W 4096 // Must be defined before next line
#include "ap_int.h"

ap_int<4096> very_wide_var;